Safety glass



Sept. 28, 1937. w. E. NOBBE 2,094,183

SAFETY GLASS Filed DeC. 5, 1955 m A /4 /Z (Ittorneg Patented sept. 2s,1937 i i -2,694,183

UNITED STATES Ysllrlrrr GLASS William E. Nobbe, Toledo, Ohio, assignorto Libbey-Owens-Ford Glass Company, Toledo, Ohio, a corporation of OhioAppliontion December 5, 1931s, serial No. 701,041 2 Claims. (Cl. 49-81)The present invention relates to composite the following descriptionwhen taken in 'connec-` safety glass and to the process of producing thetion with the accompanying drawing.

same. In the drawing, wherein like numerals are em- Safety glass,asknown today, usually comprises ployed to designate like partsthroughout the 5 two sheets of ordinary plate or window glass same, 5between which is arranged alayer of suitable Fig. 1 isa diagrammaticView 0f 011e type 0f plastic material, such as a cellulose ester, whichapparatus Wllieh may be empleyed for heating is bonded to the glasssheets. As is well known, and tempering the glass I if a single sheet ofordinary plate or window glass Fis.v 2 is a fragmentary sectional viewshowms l0 is broken by an impact, it w11l break and y into the treatedlaminations in propel' superimposed v l0 fragments of varying sizes andifbroken in the relationshipy vicinity of a person is quite apt tocause' injury Fig. 3 discloses diagrammatically a form of to suchperson. Safety glass is designed to pre- Dressing means which Can beused in the making vent the scattering or ying of the glass, and this 0fthe Composite StI'uCtule,

is accomplished by bonding the glass Asheets to Fie. 4 is a fragmentarysectional view showing 15 the intermediate plastic layer,with thethought a 'Sheet 0f finished Safety glass made in eCCOldin mind thatshould the sheet beoorne broken, the ance with the present invention,and fragments will remain adherent to the plastic, Fig. 5 is a similarview of a sheetof so-called The electiveness of the safety glass isdependbullet-PTOO gleSS- y l ent, among other things, upon the qualityof bond Referring now to the drawing and particularly between thevarious laminations. LProperly made Wtll'refel'enee rSt t0 Fg- 4, thereiS illustrated safety glass will ordinarily not release sizeable a Sheet0f 'COmPOSite Safety glass l0, including particles of glass. However,even' though the a sheet of ordinary plate or Window slass Il and glasssheets are bonded to the plastic material, f a Sheet 0f hardened 0I'tempered glass i2 bOIided when broken the glass sheets break intopartitogether by a central sheet or layer of plastic macles of varyingsizes and shapes. When impacted teiiiil i3. t0 ferm a Unitary StructurePrior i0 sufliciently hard, some of the glass may be thrown theassembling of the glass sheets, however, the from the plastic or anentire portion of th lamiinner surfaces thereof are adapted to becovered nated structure may beA separated from the bal- With 2 @Dating0f Some Suitable bending medium ance of the sheet and hurled against theOccuand various forms'of adhesives, solvents, etc., can pants of thevehicle in whiehthe glass may `19e be used as the bonding materialbetween the glass installed. and plastic. Ordinarily, a cellulose esteris used It is an impor ant object of this invention to as thenon-brittle portion of the composite sheet, provide an entirely new typeof composite safety and such cellulose esters as pyrexylin plastic andglass which, is more resistant tov breakage than cellulose acetate havebeen used satisfactorily. 35

ordinary safety glass and which, even when In carrying the inventioninto practice, the

broken, will afford a greater degree or measure oi Sheet 0f glass i2 isnfsi" Case hardened 0i' tem' protection to those who'may be in closeproximity Peiei in a manner te increase its mechanical thereto, strengthand modify its breaking characteristics. 40

40 To accomplish this, the glass sheet is first heated to asubstantially uniform temperature throughcomprises one sheet of ordinaryplate or window out' .lts thlckness .nth the tempera'tfure approxiglassand one sheet of glass which has been tem- I'lrngw evgl tgatsugeei)issfsl pered or case hardened in a manner to increase jected t0- aSudden 'cooling 0r chilling action 5 its meehanieai strength and modifyits breaking which serves to place the outer surfaces thereofcharacteristics the two sheets 0f gia'ss being under compression and itsinterior under tension. bonded together by a sheet or layer of plasticma- Glass Sheets, thus hardened or tempered, are terial interposedtherebetween. The hardened or much more resistant to breakage thanordinary tempered sheet of glass is so treated that if and plate orwindow glass. Furthermore, when imwhen broken, it will fracture into arelatively pacted sufficiently hard to cause actual breakage, largenumber of very small pieces which will r'ethe glass will shatter ordisintegrate into a largeA main adherent to the central layer ofplastic. number of very small particles or fragments, so r Other objectsand advantages of the invention that even if broken the chances ofserious injury 55 5U will become more apparent during the course of topersons nearby are greatly reduced.

Briey stated, the composite safety glass provided in accordance with thepresent invention The heating of the glass sheet I2 to a substantiallyuniform temperature throughout its thickness may be accomplished byplacing the sheet in a heating chamber I5, with the sheet beingsuspended from near its upper edge by tongs I 6. The chamber I5 may, ofcourse, be of any approved type both as regards the means of heating itand the means for feeding the sheet thereto and removing it therefrom.

After the glass sheet I2 has been brought to the desired temperature, itis withdrawn vertically from the heating chamber I5 and subjectedimmediately to a sudden cooling or chilling action to temper the same.The tempering means here shown consists of the spaced verticallydisposed cooling devices I1 and I8 respectively, positioned directlyabove the heating chamber and adapted to receive the glass sheettherebetween as it is drawn upwardly therefrom. These cooling devicesare provided with a relatively large number of small openings, fromwhich jets of air under pressure are adapted to be projected against thesheet. The jets of air impinging upon the opposite surfaces of thehighly heated glass sheet naturally cause a quick or sudden cooling orchilling thereof and results in the outer surface skins of the saidsheet being placed under compression` and the interior thereof undertension.

After the sheet has been suitably tempered, it is arranged in properlyassembled relationship with respect to the sheet of ordinary plate orwindow glass I I and the layer of plastic material I3, the layer ofplastic being interposed between the two sheets of glass. After theseveral laminations have been properly treated and assembled, thesandwich I9 thus produced, is adapted to be subjected to the action ofheat and pressure to eect the uniting thereof. For this purpose, anordinary platen press 20 of the type illustrated in Fig. 3 may be used,or, if desired, the sandwich can be preliminarily pressed by firstpassing it through a series of pairs of rollers and then finally pressedin an autoclave. 'Ihe chilling of the glass can also be accomplishedbetween cold metal surfaces or by plungingin a bath of liquid.

Although the novel and improved type of cornposite safety glass hereinprovided can be put to various uses, it has been primarily designed forthe Vwindshields and/or Windows of automotive vehicles, and when so usedit is preferable that the sheet of tempered or hardened glass be placedtoward the inside of the vehicle. This is desirable, since in the eventthe hardened sheet of glass is broken, it will break into a large numberof very small particles which will ordinarily remain adherent to theplastic. In other words, there is much less danger of these smallparticles being thrown from the plastic than is the case with ordinaryplate or window glass. if for some reason or other, some particles ofthe glass should be released from the composite structure, they will notbe of sufficient size or of such shape as to cause serious injury topersons riding in the vehicle. It has been found that when a glasssheet, tempered in the manner above described, is broken, it breaks intoa large number of particles and that no particle of glass has a greaterdiameter than one-half inch, while the majority of the particles have adiameter less than one-quarter inch. Also, it seems characteristic ofthe glass that it breaks in such a way that the particles are retainedin inter-locking relationship.

It has been demonstrated, by numerous tests, that flying pebbles orgravel have a tendency to 'fracture safety glass.

However,

, plate or window When a safety glass windshield, for instance, isimpacted with a fairly large object, the weight of the object issufficient to cause a slight bending of the windshield and even thoughthe glass cracks in the great majority of cases, no glass will leave theinner plastic. However, when light pebbles strike the windshield withbullet-like velocity, they do not possess sufficient weight to bend itand occasionally the inner sheet of glass is conchoidally fractured.That is to say, a small piece of glass will be released from within thethickness of the inner sheet of glass itself, and there is, of course,the possibility that this piece of glass may cause injury to theoccupants of the vehicle. However, by using a composite safety glasswindshield including a sheet of tempered glass, and in placing thissheet toward the inside of the vehicle, the composite sheet will notonly be more resistant to such fractures, but even should it be thusfractured, the inner tempered sheet of glass will break into very smallparticles, and even though somel of these particles may be released,they will not be of suilicient size to cause any serious injury. Thesame, of course, also holds true of the door and window lights.

It is also preferable, although not absolutely necessary, that the sheetof ordinary plate or window glass Il be relatively thinner than thesheet of hardened or tempered glass I2. The reason for this differencein thickness is so that the over-all thickness of the finished compositesheet will be very little, if any, greater than the over-all thicknessof the present safety glass sheet made of two sheets of ordinary plateor window glass and which thickness is approximately seventhirty-seconds to nine thirty-seconds of an inch. Up to the presenttime, it has L been found impractical to satisfactorily temper extremelythin sheets of glass in the manner set forth above, and in fact thethinnest sheet which can be satisfactorily treated is three-sixteenthsor six thirty-seconds of an inch. The use of two sheets of temperedglass would therefore result in a composite sheet at least twelvethirty-seconds of an inch, not including the inner sheet of p lastic.The present invention, therefore, contemplates the use of a relativelythinner sheet of plate or window glass which, when combined with thesheet of tempered glass, will result in a composite sheet ofapproximately the same over-all thickness as ordinary safety glass madeup of two sheets of plate or window glass. For instance, the sheetoftempered glass may be six thirtyseconds of an inch thick, and thesheet of ordinary plate or window glass one-eighth or fourthirty-seconds of an inch, giving an over-all thickness ofvapproximately ten thirty-seconds of an inch, which will be only onethirty-second of an inch thicker than the majority of safety glass madetoday. If desired, however, the sheet of glass can be slightly thinnerthan one-eighth of an inch so as to bring the over-all thickness of thecomposite sheet down to nine thirty-seconds of an inch or even slightlyless. This would, of course, be preferable since the improved type ofsafety glass herein provided could then be readily substituted forordinary safety glass now in use. While the composite safety glass hereprovided may be slightly more expensive to produce than ordinary safetyglass, it will possess advantages which will more than outweigh theincreased cost of production.

In Fig. 5 of the drawing, there is illustrated a sheet of so-calledbullet-proof glass 2I, made up aooaies of three sheets of glass 22, 23and 2d, bonded t0- gether by two layers of plastic material 25 and 26 toprovide a unitary structure. The central sheet of glass 23 is ofrelatively Agreater thickness than the glass sheets 22 and 24 and is.preferably of ordinary plate glass. The sheet Z, while rela; tivelythicker than sheet 22, is likewise relatively thinner than sheet 23 andis preferably of hardened or tempered glass, While the sheet 22 may beof ordinary plate or Window glass. If preferred, however, the innersheet of glass' 23 may also be tempered or hardened. When used as ashield, it is preferred that the sheet of hardened glass 24 be placedupon the inside.

In the claims, the term sheet glass is used in a generic sense to meaneither plate glass which is ground and polished, or Window glass whichis not ground and polished.

I claim:

1. A composite safety ,glass sheet including a layer of plastic materialfaced on both sides with adherent plates of glass, one of said plates of`glass only being case hardened to modify its breaking characteristicswhile the other plate is ordinary sheet glass'.

2. A composite safety glass sheet including two plates of glass and aninterposed layer of plastic material bonded thereto, one of said platesof glass only having its outer surfaces under compression and itsinterior under tension while the other plate is ordinary sheet glass.

WI E. NOBBE.

